The present invention relates to a driving apparatus for driving or actuating a driven unit in association with a driving power source, and more particularly to a driving apparatus with an automatic speed ratio change device which automatically changes the speed ratio of a driven shaft to a driving shaft in response to the rotational speed thereof. The present invention also relates to a driving method in which a driven unit is rotated in association with a driving power source at a changeable rotational speed ratio changing in response to the rotational speed of the driving power source.
An automotive vehicle is provided with various auxiliary machineries such as an alternator, a cooling fan and a water pump, etc., all of which are driven by an internal combustion engine. Conventionally, these auxiliary machineries have been driven through belts at a rotational speed in proportion to that of a driving shaft of the engine.
However, it has been required recently from the view-point of the durability of the auxiliary machinery as well as the power expenditure of the engine to lower the speed ratio of the auxiliary machinery to the engine as the engine speed increases and to maintain the speed of the auxiliary machinery substantially at a constant value. For example, the alternator should be driven within a speed range below a predetermined value so as to insure the durability thereof, since the alternator output characteristic in which the output current becomes substantially constant when the rotational speed of a rotor exceeds the predetermined value. The cooling fan may also be driven at about a constant speed in a common speed range of the engine.
There is known in the art a driving apparatus with a speed change device which includes at least two pairs of pulleys having different diameter-ratios and belts interconnecting the pulleys. In this apparatus, one pair of pulleys is connected to a driven shaft and a driving shaft while the other pair of pulleys is released from the shafts in the low speed range; the second pair of pulleys is connected to the shafts in the high speed range.
By this apparatus, however, the speed ratio of the driven shaft to the driving shaft is abruptly changed. The belts and the auxiliary machinery are shocked by this abrupt change in the speed ratio and may possibly be broken. Further, it is impossible for this apparatus to maintain the rotational speed of the auxiliary machinery at a substantially constant value.